How to add grub boot item to installation usb when it's read-only?

[left4taco]

I need to install ubuntu on multiple machines so preseed would be very useful.
Here's the grub item that I would like to add,


menuentry "DANGER! This will reprovision you machine" { set gfxpayload=keep
echo "Please enter your device type(desktop, spectra):"
read device
echo ""
echo "Please enter the hosename of the new machine:"
read hn
linux /casper/vmlinuz url=http://x.x.x.x:5000/preseed/$device/$hn boot=casper debian-installer/locale=en_US keyboard-configuration/layoutcode=us ubiquity/reboot=true languagechooser/language-name=English countrychooser/shortlist=US localechooser/supported-locales=en_US.UTF-8 automatic-ubiquity quiet splash noprompt noshell ---
initrd /casper/initrd

}


However, after I followed the official tutorial of creating bootable usb stick, it's always write protected which means I can only mount it as readonly. The partition table is like:



sdb 8:16 1 29.3G 0 disk
├─sdb2 8:18 1 2.4M 0 part
└─sdb1 8:17 1 1.6G 0 part


So in this case, how can I create a bootable usb stick while being able to copy files to it?


========
Solved. Format the disk to FAT and copy everything from ISO. It's now both bootable and writable.

[yancek]

Is that a typo and you meant "NOW" both bootable and writable rather than not?

Loop mounting the iso and then copying it to a partition on the usb should work to modify and it doesn't need to be a FAT filesystem.
Another method would be to create a boot directory on the usb and then install Grub to the usb and manually modify grub.cfg. This method allows you to simply copy the iso to a partition on the usb.

[C.S.Cameron]

@left4taco
Your system works on UEFI boot but not on older BIOS boot computers.
Mkusb builds a nice grub2 drive that boots both BIOS and UEFI.
Sdx4, the ISO9660 OS partition can be replaced with anything from ISO files to a clone of your desktop system.
The grub.cfg file in sdx2 can be edited to boot them.

[left4taco]

Yes `not` is a type and has been fixed. I'll look into your second solution. Thanks.